“I had been reading about all of the controversy surrounding solitary confinement, and the fact that it’s been subject to congressional hearings an UN reports,” Harris told TVNewser. “I thought it was a really important story, because we have 80,000 people locked up in solitary in this country.”

Harris and a team of producers began reaching out to jails with solitary confinement facilities across the country, trying to persuade them to allow Harris in to report for “Nightline.” The Denver County Jail was one of the only in the country to agree, and in June, Harris packed his bags for two days as a solitary prisoner.

“I was somewhat cocky going in, I have to say. I assumed that 48 hours without a Blackberry, without phone calls, without having to do any work, would be uncomfortable but mildly pleasant because I would relax,” Harris told TVNewser. “It turned out to be probably two of the worst days of my life.”

The facility in Denver houses about 100 solitary prisoners, and Harris said the people around him were “howling, banging against the doors.”

“The jail we were in was very modern — very cold, no privacy, there’s no darkness ever,” he said. “There’s just a thin blanket and no pillow. And the worst part of it is the boredom, the absolutely mind-crushing boredom.”

Solitary confinement is three times more expensive, and significantly more controversial, than housing other prisoners, Harris said.

“We’re paying for it, and there are a lot of experts who argue that its legalized torture,” Harris said. “We’re not coming down on one side or another, but the bare facts are important for people to know. TV at its best takes you to a place you would never otherwise see and you probably ought to know about.”

Watch a preview of Harris’ report, which airs tonight on “Nightline,” here: